Critical Current Density and Resistivity of MgB2 Films

TL;DR

This paper investigates the relationship between critical current density and resistivity in MgB2 films, proposing a correlation that explains how effective current-carrying area impacts superconducting properties.

Contribution

It introduces a correlation between Jc and resistivity change, supported by measurements on MgB2 films, extending the understanding to bulk and wire samples.

Findings

Jc correlates with 1/{Rho(300K) - Rho(50K)}

Measured resistivity and Jc support the proposed correlation

Porosity and grain boundary oxides affect effective current-carrying area

Abstract

The high resistivity of many bulk and film samples of MgB2 is most readily explained by the suggestion that only a fraction of the cross-sectional area of the samples is effectively carrying current. Hence the supercurrent (Jc) in such samples will be limited by the same area factor, arising for example from porosity or from insulating oxides present at the grain boundaries. We suggest that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K) - Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We report measurements of Rho(T) and Jc for a number of films made by hybrid physical-chemical vapor deposition which demonstrate this correlation, although the "reduced effective area" argument alone is not sufficient. We suggest that this argument can also apply to many polycrystalline bulk and wire samples of MgB2.